1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD), and more particularly, to a liquid crystal display device having a common-auxiliary electrode.
2. Description of the Related Art
Recently, an LCD has been proposed where the liquid crystal is not aligned and the liquid crystal is driven by side-electrodes insulated from pixel electrodes. FIG. 1 is sectional view of pixel unit of the conventional LCDs.
Regarding conventional LCDs, a plurality of gate bus lines arranged in a first direction on a first substrate and a plurality of data bus lines arranged in a second direction on the first substrate divide the first substrate into a plurality of pixel regions. A thin film transistor (TFT) applies image signal delivered from the data bus line to a pixel electrode 13 on a passivation layer 37. The TFT is formed on each pixel region and comprises a gate electrode, a gate insulator, a semiconductor layer, a source electrode, and a drain electrode, etc. Side electrode 15 is formed surrounding the pixel electrode 13 on the gate insulator, thereon passivation layer 37 is formed over the whole first substrate, and a part of pixel electrode 13 overlaps side electrode 15.
Alternatively, pixel electrode 13 is formed on the gate insulator, and passivation layer 37 is formed over the whole first substrate.
On second substrate, a common electrode 17 is formed and together with pixel electrode 13 applies electric field to a liquid crystal layer. Side electrode 21 and open area (slit) 27 distort the electric field applied to the liquid crystal layer. Then in a unit pixel liquid crystal molecules are driven variously. This means that when voltage is applied to the LCD, dielectric energy due to the distorted electric field arranges the liquid crystal directors in needed or desired positions.
In the LCDs, however, open area 27 in common electrode 17 or pixel electrode 13 is necessary, and the liquid crystal molecules could be driven stably when the open area is wider. If the electrodes do not have an open area or the width of the open area is narrow, the electric field distortion needed to divide the pixel region becomes weak. Then, when voltage over a threshold voltage, Vth, is applied, the time needed to stabilize the liquid crystal directors increases. In particular, the response time can be over 100 msec. At this time, disclination occurs from the area where the liquid crystal directors are parallel with a transmittance axis of the polarizer, which results in a decrease in brightness. Further, according to the surface state of LCDs, the liquid crystal texture has an irregular structure.
Furthermore, in the conventional LCDs, although a storage electrode is formed on the gate bus line to maintain the voltage applied to the pixel electrode, there are still the problems of filters resulted from the shortage generated between the gate bus line and the storage electrode.